This invention relates to manual drilling apparatus, and more particularly to apparatus for drilling into the end of a metallic prosthesis fragment which remains securely embedded in skeletal bone after fracture of the prosthesis and removal of the relatively free portion of the fractured prosthesis.
Possibly as the result of an accident or a war injury, or the crippling effects of bone disease, it is sometimes desirable to replace a joint of the human body with an artificial joint. The total replacement of joints, and the consequent possibility of a future revision of a surgically implanted joint, is a relatively new field of surgery. Its development is being enhanced by the discovery, and application in the surgery field, of newer and stronger metals and of new plastics and similar materials. For example, a total hip replacement consists of replacing the existing acetabular cup with a polymer polyethylene plastic cup, and replacing the rounded head of the femur with a metal prosthesis including a ball which coacts with the plastic cup and an elongated stem which is extended into and embedded in the intramedullary canal of the femoral shaft. Even though this metal femoral component of the prosthesis is constructed of extremely hard metal, because of all of the stress and strain that is placed upon it by the action of the human body in the performance of its daily routine, it sometimes happens that the shaft of the prosthesis will fracture; and replacement of the entire femoral component will then be necessary in order to allow the wearer to remain ambulatory without experiencing considerable pain. The difficulty of extracting the tip portion of a fractured prosthesis stem is readily apparent when one considers that this tip portion is implanted possibly deep within the intramedullary canal of the bone and possibly embedded within surgical cement, and that the surgical area is confined considering the narrow size of the bone shaft.
This invention is particularly concerned with the aspect of revision surgery which involves the removal of an earlier implanted prosthesis which has fractured, in order to enable implantation of a replacement prosthesis. While the invention is concerned broadly with drilling apparatus, the invention will be described with particular reference to hip revision surgery.
One approach which has been used in the past to remove the embedded tip of the femoral stem of a hip joint prosthesis involves the removal of the surgical cement from the annular space between the stem and the femoral cortex. Tools for this procedure may include osteotomes or power instruments. Because this annular space is usually very narrow, it may be difficult to remove the cement around the broken stem for a distance sufficient to allow it to be dislodged. Moreover, because of this confined space, a frequent complication of this procedure is the perforation of the cortex. This complication may require bone grafting and the use of a long-stem femoral component for the revision implant. The use of such long stem femoral component further compounds the complication, since the achieving of excellent cement distribution and pressurization is much more difficult with the use of such long-stem component, especially if there is a hole in the femur. In addition, the future surgical revision of the long-stem femoral component, should it fail, increases the technical difficulties.
Another known approach for the removal of the embedded tip of a prosthesis stem involves creating a window in the cortex of the femur to enable the driving of the stem toward the cut surface of the femoral neck through the use of a driving tool such as a carbide chisel. One complication of this procedure is that the creating of the window in the femur produces a stress riser which weakens the femur and predisposes this area to fracture. To overcome the resulting femoral weakness, it is necessary to use a long-stem component for the replacement prosthesis, in order to bypass the stress riser. Complications accompanying the long-stem component have been discussed above. Accessory fixation and/or bone grafting may also be required. With this approach, a possible mechanical problem may result from the use of extremely hard so-called space-age metals in the fabrication of the original prosthesis. With such metals it is sometimes difficult, even with a carbide tip chisel, for example, to penetrate the surface of the prosthesis sufficiently to enable it to be driven by the chisel.
The concept of drilling into the fractured proximal end of the embedded prosthesis tip and locking into that drilled hole with some form of extractor device to enable withdrawing of the prosthesis tip, without resorting to either of the above described techniques or approaches, is attractive. One known technique, embodying this concept, involves drilling into the distal end of the stem and utilizing a screw threadedly engaged within the drilled hole as an extractor. While this technique may be useful where the prosthesis has been fabricated from stainless steel or other material having the equivalent or lesser hardness, this technique is not suited for use with prostheses constructed of the harder spage-age metals and alloys.